The mathematics of pandemics

There's been a lot of coverage on how people are still not getting the message about keeping your distance and minimising contact with others. I guess a lot of people are wondering what difference their contribution might make - even if they were infectious. And anyway, isn't it all like flu which comes round every year?

“If you are irresponsible enough to think that you don’t mind if you get the flu, remember it’s not about you - it’s about everybody else.”

Intensive care specialist Professor Hugh Montgomery explains why this coronavirus is different from the ordinary flu. pic.twitter.com/h9sQorHQUv

— Channel 4 Dispatches (@C4Dispatches) March 22, 2020

If you haven't got time to watch the video, or you didn't follow it, here's the calculation.

On average someone with flu infects 1.3 people (OK there's no such thing as 1.3 people, but it's an average)

If that infection process happens 10 times over then 1.3x1.3..  [ten times over] = 13.78. Let's call it 14.

On the video he says flu infects 1.3-1.4 on average. Put 1.4 in the equation and you get 28.9. Let's call that 29. That's double.

But if a virus is more easily transmitted, each person with it will infect more. Let's see what happens if a bug meant each infected person passed it on to 2 more people, and that happened 10 times over

2 x 2 = 4
2 x 2 x 2 = 8
...
2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 1024

According to Professor Montgomery, with covid-19 the it's 3 people. And if you put 3 into the calculation, you get:

59049

That's right. Over 59,000 people infected. And that's why it's important to close off as many avenues as possible for this thing to spread.